1. Field of the Invention
The present invention relates to a method for manufacturing carbon nanocoils that comprise carbon atoms grown in a spiral form and have an outside diameter of 1000 nm or less and more particularly to a method for mass-producing carbon nanocoils that makes carbon nanocoils grow efficiently on a surface of catalyst by decomposing thermally hydrocarbon gas using indium/tin/iron-based catalyst.
2. Prior Art
In 1994 Amelinckx et al. (Amelinckx, X. B. Zhang, D. Bernaerts, X. F. Zhang, V. Ivanov, and J. B. Nagy, Science, 265 (1994), 635) succeeded at producing carbon nanocoils. Whereas the carbon microcoils that had been produced up to that point had an outside diameter on the micron order and furthermore were amorphous, it was revealed that the carbon nanocoils have a graphite structure. Various types of carbon nanocoils were produced thereafter, and the smallest coil diameter achieved was extremely small (about 12 nm). However, the coil yield remained so low that the process of manufacturing such carbon nanocoils was unfeasible for industrial production. Thus, there has been a need for a more efficient manufacturing method.
The above-mentioned manufacturing method involved the steps of forming a micropowder of a metal catalyst such as cobalt, iron or nickel, heating the area near this catalyst to between 600 and 700° C., and sending an organic gas such as acetylene or benzene through the manufacturing system so as to come into contact with the catalyst. However, this method was not utilized industrially because of its extremely low coil yield.
In 1999 Li et al. (W. Li, S. Xie, W. Liu, R. Zhao, Y. Zhang, W. Zhou, and G. Wang, J. Material Sci., 34 (1999), 2745) succeeded a new producing method of carbon nanocoils. They placed a catalyst in the center of a graphite sheet covered around its outer periphery with iron particles and heated the catalyst to 700° C. while passing a mixed gas of acetylene and nitrogen over the catalyst, so that carbon nanocoils were produced on the catalyst surface. Unfortunately, this manufacturing method also results in a coil yield so low as to be unfeasible for industrial production.
The development of a suitable catalyst is the key to raising the carbon nanocoil yield. In view of this, the inventors of the present application examined various catalysts in an effort to increase the carbon nanocoil yield and succeeded in obtaining a yield of 90% or higher by using, in particular, an indium/tin/iron-based catalyst. The results of this research were disclosed in Japanese Patent Application Laid-Open Nos. 2001-192204 and 2001-310130.
The inventions in such applications proved the effectiveness of an indium/tin/iron-based catalyst. What was needed next was the development of a method for mass-producing carbon nanocoils using this indium/tin/iron-based catalyst or in other words, a continuous production method.